This invention relates to a nickel-metal hydride/Hydrogen hybrid battery that includes a non-porous, alkali ion conducting separator.
Nickel-metal hydride storage batteries are widely used for the power sources of cordless electronic equipment, power tools, electric vehicles and the like. Conventional nickel-metal hydride batteries are composed of a positive electrode containing nickel hydroxide, a negative electrode containing a hydrogen-absorbing metal alloy, a microporous separator interposed between the positive and negative electrodes, and an electrolyte.
Nickel hydrogen battery (Ni—H2) is a choice battery in many aerospace applications, especially geo-synchronous (GEO) and low earth-orbit (LEO) satellites. Recently, nickel-hydrogen batteries have also been used in terrestrial applications. The difference with a nickel-metal hydride battery is the use of hydrogen in a pressurized cell of up to 1200 psi (82.7 bar). The Ni—H2 battery comprises a positive electrode containing nickel hydroxide, a negative hydrogen electrode utilizes a teflon-bonded platinum black catalyst, and a zirconia cloth separator. This battery has a long cycle life, high specific energy, high power density, and also exhibits tolerance for overcharge. Its disadvantages include an expensive initial cost, as well as low volumetric energy density.
Self-discharge is a phenomenon in many rechargeable batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes. Self-discharge decreases the shelf-life of batteries and causes them to have less charge than expected when actually put to use. How fast self-discharge in a battery occurs is dependent on the type of battery and temperature. Nickel-based batteries typically are significantly affected by self-discharge (nickel cadmium, 15-20% per month; nickel metal hydride, 30% per month; nickel hydrogen proportional to hydrogen pressure). Self-discharge is a chemical reaction and tends to occur more quickly at higher temperatures. Storing batteries at lower temperatures may reduce the rate of self-discharge and preserve the initial energy stored in the battery.
Without being bound by theory, it is believed the self-discharge problem associate with nickel metal hydride batteries is a result of hydrogen passing through the porous separator.
It would be an improvement in the art to provide a nickel metal hydride battery with reduced or limited self-discharge.